482 Mason . — Growth and Abscission in Sea Island Cotton . 
finally shed. That the destruction of pollen by rain was responsible 
for a small proportion of the shedding there would seem to be no 
doubt, but the more generally constant cause, it was concluded, was due 
to an interruption in the supply of assimilates entering the boll during 
the critical stage of growth-retardation which followed anthesis. The 
occurrence of a check in the growth-rate at this period seemingly prevents 
a variable proportion of the bolls from undertaking the augmented growth 
of the second stage, in spite of fertilization. Inasmuch as the factors 
responsible for the movement of elaborated food in the plant are still quite 
unknown, it is useless to speculate as to why one boll is able to survive 
while a neighbouring one undergoes abscission. The phenomena of physio- 
logical correlation are presumably in some way responsible. 
Before concluding, it is important to note that negative growth-rates 
are normally shown for some one to three days prior to the completion of 
abscission. It would seem that the failure to secure the normal supply 
of assimilates must diminish the water-absorbing power ( 7 ) of the boll until 
a stage is reached at which the tension in the water columns of the plant 
leads to a suction of water from the boll. It may well be that this is not 
only the cause of" the negative growth-rates, but that it is actually the factor 
which initiates abscission. It will be evident that any factor which injures 
the boll — insect punctures, fungous diseases, &c. — will bring about abscission, 
provided the injury is sufficiently pronounced as to interrupt the movements 
of elaborated food into the boll. 
Summary. 
1. A survey was made of the external and internal factors affecting 
the shedding of bolls and flower-buds in St. Vincent. 
2. The susceptibility to shedding is relatively small in the earlier stages 
of the flowering period, but becomes much more marked in the later stages. 
It was found that the susceptibility becomes especially pronounced after the 
occurrence of growth-cessation in the main axis. 
3. Both the cessation of growth in the main axis and the augmented 
susceptibility to shedding were attributed to a correlation factor which 
tended to deflect the supply of elaborated food from the apical part of the 
plant to the fruit developing on the basal fruiting branches. 
4. The growth rate of the main axis was retarded on overcast, humid 
days. Periods of daytime rain, low rates of evaporation, and little 
direct solar radiation were also the precursors of augmented rates of 
shedding. 
5. The retardation in the growth-rate of the main axis and the 
augmented rates of shedding were both attributed to a check in the 
assimilative activity of the leaves. 
